Biomedical Engineering Reference
In-Depth Information
method is that it is one of the more convenient
and straightforward methods for preparing
porous 3D scaffolds. The technique involves a
minimal number of steps and only requires
basic laboratory methods.
One of the major drawbacks to salt leaching
is that it only produces thin membranes with a
dense surface skin. Moreover, the bioscaffold
might contain residual salt particles used during
the process. This could negatively impact cell
behavior and ultimately tissue growth. In addi-
tion to residual salt or other particles remaining
on the scaffold, there is often incomplete removal
of the solvent during the drying process. Another
disadvantage of this method (and other meth-
ods employing polymers) is that some of the
polymers degrade into acidic by-products.
These acidic degradation products could poten-
tially have negative effects on cell adhesion and
growth
[50]
. Finally, another potential drawback
to the salt-leaching technique, especially for
bioscaffolds needing lower porosity levels, is the
lack of interconnectivity between pores. Salt
particles that are not in contact with other par-
ticles lead to insufficient pore interconnectivity
and often become trapped in the polymer scaf-
fold
[51]
.
To ameliorate the aforementioned problems,
researchers have investigated means to make
the process more benign. One method that has
been employed is the use of melt polymer solu-
tions for the solvent-casting stage, as opposed to
using a polymer solution with harsh organic
solvents. The melt-molding step consists of mix-
ing the polymer powder with salt particles and
melting the mixture
[81]
. The melting step elimi-
nates the need for organic solvents, thereby pre-
venting the possibility of the scaffold containing
residual solvent and harming cells or tissue.
In an attempt to create better interconnectiv-
ity between pores and to increase the channel
size between pores, a method where by salt par-
ticles are partially merged has been proposed.
This method involves merging salt particles
processes used to produce the various types of
3D scaffolds by traditional and recently devel-
oped fabrication techniques.
7.2.1 Conventional Scaffolds
Several conventional techniques used to produce
porous scaffolds, including the salt-leaching
and gas-foaming methods, have been used to
introduce open pore structures and intercon-
nected channels within bioscaffolds. Pores are
important to increase the viability of seeded or
injected cells within the scaffolds
[73-76]
. These
traditional techniques for preparing 3D scaf-
folds are straightforward, cost-effective, and
easy to scale up
[77, 78]
.
7.2.1.1 Salt-Leaching Method
Salt-leaching
is a simple processing technique to
produce 3D biomimetic scaffolds. This method
involves making a polymer/organic solvent
solution and incorporating porogen particles,
which are insoluble in the organic solvent. The
solution is then cast into a mold of the desired
shape, and the solvent is evaporated away. After
the solvent completely evaporates, the final step
is to dissolve the porogen particles in an aque-
ous solution
[49, 50]
. The resulting structure has
significant porosity as a result of the void spaces
left by the dissolved porogen particles. Typi-
cally, the porogen is a salt granule or particle.
As with all techniques, there are advantages
and disadvantages in using this method. One
of the main advantages is that porosity and
pore size can be effectively controlled. Materi-
als with porosity levels up to 90% and pore-size
diameter ranging from 100 to 700
μ
m have been
reported using the salt-leaching technique. The
porosity is given by volume fraction occupied
by leachable particles. The pore size and pore
shape can be modified independently of the
porosity by varying the leachable particles'
characteristics (i.e., size and shape)
[51, 79, 80]
.
Another advantage of using the salt-leaching
